Solid-state imaging workstations, that are configured either as vertical slot scanners each having a generally vertically arranged, upright window, or as flat-bed or horizontal slot scanners each having a generally horizontally arranged window, or as bi-optical, dual window scanners each having both generally horizontally and vertically arranged windows, or as stand-mounted, stationary scanners having a presentation window, have been installed in many venues, such as supermarkets, department stores, and other kinds of retailers, as well as warehouses, and other kinds of industrial settings, for many years, to electro-optically read by image capture a plurality of symbol targets, such as one-dimensional symbols, particularly Universal Product Code (UPC) bar code symbols, and two-dimensional symbols, as well as non-symbol targets, such as driver's licenses, receipts, signatures, etc., the targets being associated with objects or products to be processed by the workstations. An operator or a customer may slide or swipe a product associated with, or bearing, a target in a moving direction across and past a window of the workstation in a swipe mode. Alternatively, the operator or the customer may momentarily present the target associated with, or borne by, the product to an approximate central region of a window, and steadily momentarily hold the target in front of the window, in a presentation mode. The choice depends on user preference, or on the layout of the workstation, or on the type of the target.
Known imaging workstations typically include an imaging scan engine or module for supporting a solid-state, image sensor or imager comprising an array of pixels or photosensors, for sensing return light returning through a window of the workstation from a target being imaged. The image sensor may be a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device, operable at a frame rate, and is analogous to the image sensors used in electronic digital cameras. The known imaging workstations also typically include an illuminating light system for illuminating the target with illumination light from an illumination light source, e.g., one or more light emitting diodes (LEDs), through the window of the workstation; an imaging lens assembly, e.g., one or more imaging lenses, for capturing return ambient and/or illumination light scattered and/or reflected from the target through the window of the workstation over a reading field of view and over a range of working distances relative to the window; and electrical circuitry for producing electronic analog signals corresponding to the intensity of the light captured by the image sensor over the reading field of view, and for digitizing the analog signal. The electrical circuitry typically includes a controller or programmed microprocessor for controlling operation of the electrical components supported by the workstations, and for processing the target and/or decoding the digitized signal based upon a specific symbology when the target is a symbol.
Some known workstations continuously capture and attempt to process and/or decode targets without regard to whether or not a target is actually in the reading field of view of the scan engine. However, continuous, repetitive, flashing of bright light from the LEDs of the illuminating light system consume and waste energy, degrade component lifetimes, and can be perceived as bothersome, distracting and annoying to the operators of the readers and to nearby consumers being served. To alleviate these problems, the known imaging workstations also typically include an object sensing system for activating the scan engine, e.g., the illuminating light system, only if an object or product bearing, or associated with, a target is detected within the active reading field of view of the scan engine. The object sensing system has one or more object light sources for emitting object sensing light, typically infrared (IR) light, and at least one object sensor for sensing the return IR light reflected and/or scattered from the object over an object detection field of view.
The known imaging scan engine is typically configured to operate in real time to process and decode a symbol target as quickly as it can within each and every single frame of the image sensor. For example, if the image sensor operates at a nominal frame rate of about 60 frames per second, then the fastest frame lasts about 16.67 milliseconds. In this case, the imaging scan engine works in real time to process, decode and successfully read a symbol target in a minor fraction of a single one of the fastest frame, e.g., less than 1 millisecond, and preferably less than 0.5 milliseconds. This is generally satisfactory for aggressive, fast reading performance. However, there are certain situations where such fast performance cannot be readily realized.
For example, sometimes more time is needed to successfully read the symbol target. Thus, the symbol target may be poorly printed, or poorly or not illuminated, or poorly presented to the window, or be located too far from the window, or be encoded with a great deal of information (e.g., two-dimensional symbols), or be of a symbol density and size that requires extensive processing time, etc. In these and other circumstances, the known imaging scan engine may need more than one frame to process, decode and successfully read the symbol target and, indeed, may need several frames. When a particular symbol target takes longer than a single frame to analyze, its captured image might be discarded early, thereby missing the opportunity to successfully read the captured image if only there were sufficient time. Or, the scan engine might spend more time than one frame trying to analyze the captured image of the particular symbol target, in which case, the scan engine might have missed looking at a subsequent frame in which the captured image might have been more successfully decodable. Also, once a symbol target has been read, the scan engine might miss several frames while negotiating communication with a remote host computer in order to report the reading of that target, in which case, these missing frames represent more lost opportunities to read more targets.
These problems of missing frames, dropped images, insufficient processing time and loss of decodable information are magnified in many applications where multiple targets associated with multiple products are passed in a single pass through a workstation in groups or reading sessions. For example, the products may be automatically conveyed on a conveyor rapidly past a workstation window at a fast rate of speed, e.g., 100 inches per second and faster, or, the products may be manually conveyed past a workstation window in a single pass at a speed faster than the scan engine can indicate a successful reading for each target.
Accordingly, there is a need for an apparatus for, and a method of, reading all the targets presented to a workstation in a reading session with good, single-pass performance, without suffering from missing frames, dropped images, insufficient processing time and loss of decodable information.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.